Seats of various vehicles such as automobiles are provided with a seat belt apparatus in order to restrain an occupant with a seat belt and to inhibit inertial movement in the event of emergency such as a collision when a deceleration larger than during normal driving is exerted on the vehicle. Such a seat belt apparatus includes, in order to simplify the operation to put on the seat belt performed by the occupant, generally, a tongue supported by the seat belt, and a buckle that is fixed to the vehicle body and into which this tongue is inserted and latched.
A buckle including a latch member that, when a tongue is inserted, enters an engagement hole of the tongue and is engaged with the tongue, a release operation member that causes the latch member to exit from the engagement hole of the tongue and releases the latch member from engagement with the tongue, an ejector that, when the release operation member releases the latch member from engagement with the tongue, presses the tongue in a direction in which the tongue separates from the buckle, and an ejector spring that always urges the ejector in a direction in which the tongue separates from the buckle, is known as a buckle used in conventional seat belt apparatuses (see, for example, PTLs 1 and 2).
In a seat belt apparatus including this type of buckle, when an occupant puts on a seat belt, the tongue is inserted into the buckle, the latch member is engaged with the tongue, and the tongue is thereby engaged with the buckle. Thus, the seat belt is put on by the occupant. In the event of emergency described above, the occupant is restrained by the seat belt, and therefore their inertial movement is inhibited. When the seat belt is taken off by the occupant, the release operation member is pressed by the occupant, and the engagement of the latch member with the tongue is thereby released. The ejector pushes the tongue out of the buckle owing to the urging force of the ejector spring. Thus, the seat belt is taken off of the occupant.